Remarkable advancements have been made in the miniaturization and automation of camera equipment as a result of progress in the precision electronics industry. At the same time ever higher picture quality is required from sensitive materials and the level of performance demanded of the sensitive materials has now reached a very high level. Other factors influencing the course of development of the photographic art include todays preference for simplicity and speed, and the world-wise concern over the depletion of resources and the need for conservation of resources.
Many techniques are known for improving the sharpness of silver halide color photographic materials. One such technique involves reducing the amount of light which is scattered on striking the silver halide grains which are dispersed at random in a gelatin binder in the sensitive material. As disclosed in U.S. Pat. No. 3,409,433, for example, this method involves adding a colored material such as a dye to the silver halide emulsion layer or to a layer which is adjacent to the silver halide emulsion layer in order to absorb the light which is scattered by the silver halide grains. However, with methods of this type the light which should be absorbed by the silver halide grains is also absorbed and this is disadvantageous in that the speed of the light-sensitive emulsion layer is inevitably reduced.
Another technique involves the use of DIR couplers as disclosed, for example, in U.S. Pat. Nos. 3,227,554 and 4,248,962 and in Japanese patent application (OPI) Nos. 151944/82 and 217932/83 (the term "OPI" as used herein refers to a "published unexamined Japanese patent application"). In this case development inhibiting compounds are released by reaction with the oxidized form of the developing agent and sharpness is improved by an adjacency effect (edge effect) at the boundaries between exposed and unexposed areas. However, DIR couplers inhibit the development of both the layer to which they have been added and the adjacent layers and so they undesirably reduce the extent of color formation in the adjacent layers. Hence, if these compounds are used in large quantities the thickness of the light-sensitive material has to be increased since more silver halide or dye forming agent (coupler) must be used to adjust the tonality of the sensitive material and much effort is required to discover an appropriate method for the use of these materials.
Yet another technique which has been proposed as a means for improving sharpness involves reduction of the thickness of photographic emulsion layers and thereby the reduction of light scattering.
Thus, sharpness can be improved by reducing the layer thickness, by adding couplers to the developer beforehand and using external couplers to form a dye image during development, but this method is inappropriate for a coupler-incorporated type of sensitive material.
Needless to say in this case the thickness of the top layer furthest away from the support has an effect on the lower layers which are closer to the support.
Color photographic materials usually have the red, green and blue-sensitive layers coated in this order from the side closest to the support and a reduction in the thickness of the uppermost, blue-sensitive, layer is effective for improving sharpness.
The thickness of each layer of a multilayer silver halide color photographic material is determined principally by the amount of gelatin which is used for the medium, the amount of coupler used and the amount of high boiling point organic solvent which is used for dispersing the organic materials in the gelatin, and it is possible to reduce the layer thickness by reducing the amounts of these materials.
However, any reduction in the amount of coupler results in a reduction in color density and so the extent of any such reduction is obviously limited. However, there are methods in which the coupler volume is reduced by using low molecular weight couplers such as those as disclosed in Japanese patent application (OPI) No. 72243/86, but this reduces the fastness of the couplers to diffusion and may have an adverse effect since interaction with the silver halide grains is liable to occur in the emulsion layer and problems may also arise as a result of diffusion of the coupler within the layer.
On the other hand, any reduction of the amount of high boiling point organic solvent in which the organic materials are dispersed in the gelatin generally reduces the color forming potential of the couplers and may also result in a loss of stability of the dispersed couplers in the gelatin film and this is disadvantageous in that precipitation may occur in either the emulsified material or the coated film. Furthermore, with some couplers any reduction in the amount of high boiling point organic solvent may result in a marked reduction in the stability of the dyes from which the image is formed after development.
Reducing the amount of gelatin is the most effective way of reducing layer thickness but any reduction in the amount of gelating which functions s a binder results in marked changes in the properties of the gelatin film and is disadvantageous in that it leads to a deterioration of the film quality. Thus, in terms of the dynamic properties it results in a lowering of the elastic modulus and it also leads to problems with poor retention of the dispersed organic materials (sweating) in the light-sensitive layer under conditions of high temperature and humidity because of the reduced amount of binder. The improvement of sharpness by simply reducing the thickness of the material (reducing layer thickness) in this way can only be carried out within the limitations described above and it has not been possible to achieve really satisfactory results in this way.